1. Field of the Invention
This invention relates to 9-desoxoerythromycin compounds, methods of making them, and their use as prokinetic agents.
2. Description of Related Art
Gastrointestinal (“GI”) motility regulates the orderly movement of ingested material through the gut to ensure adequate absorption of nutrients, electrolytes, and fluids. Proper transit of the GI contents through the esophagus, stomach, small intestine, and colon depends on regional control of intraluminal pressure and several sphincters, which regulate their forward movement and prevent back-flow. The normal GI motility pattern may be impaired by a variety of circumstances, including disease and surgery.
GI motility disorders include gastroparesis and gastroesophageal reflux disease (“GERD”). Gastroparesis, whose symptoms include stomach upset, heartburn, nausea, and vomiting, is the delayed emptying of stomach contents. GERD refers to the varied clinical manifestations of the reflux of stomach and duodenal contents into the esophagus. The most common symptoms are heartburn and dysphasia, with blood loss from esophageal erosion also known to occur. Other examples of GI disorders in which impaired GI motility is implicated include anorexia, gall bladder stasis, postoperative paralytic ileus, scleroderma, intestinal pseudoobstruction, irritable bowel syndrome, gastritis, emesis, and chronic constipation (colonic inertia).
Motilin is a 22-amino acid peptide hormone secreted by endocrine cells in the intestinal mucosa. Its binding to the motilin receptor in the GI tract stimulates GI motility. The administration of therapeutic agents that act as motilin receptor agonists (“prokinetic agents”) has been proposed as a treatment for GI disorders.
The erythromycins are a family of macrolide antibiotics made by the fermentation of the Actinomycetes Saccharopolyspora erythraea. Erythromycin A, a commonly used antibiotic, is the most abundant and important member of the family.

The side effects of erythromycin A include nausea, vomiting, and abdominal discomfort. These effects have been traced to motilin receptor agonist activity in erythromycin A (1) and, more so, its initial acid-catalyzed degradation product (5). (The secondary degradation product, spiroketal (6), is inactive.)

Spurred by the discovery of motilin agonist activities in erythromycin A and degradation product (5), researchers have endeavored to discover new motilides, as macrolides with prokinetic activity are called. Much of the research has centered on generating new erythromycin analogs, either via post-fermentation chemical transformation of a naturally produced erythromycin or via modification (including genetic engineering) of the fermentation process. Illustrative disclosures relating to motilides based on an erythromycin scaffold include: Omura et al., U.S. Pat. No. 5,008,249 (1991) and U.S. Pat. No. 5,175,150 (1992); Harada et al., U.S. Pat. No. 5,470,961 (1995); Freiberg et al., U.S. Pat. No. 5,523,401 (1996); U.S. Pat. No. 5,523,418 (1996); U.S. Pat. No. 5,538,961 (1996); and U.S. Pat. No. 5,554,605 (1996); Lartey et al., U.S. Pat. No. 5,578,579 (1996); U.S. Pat. No. 5,654,411 (1997); U.S. Pat. No. 5,712,253 (1998); and U.S. Pat. No. 5,834,438 (1998); Koga et al., U.S. Pat. No. 5,658,888 (1997); Miura et al., U.S. Pat. No. 5,959,088 (1998); Premchandran et al., U.S. Pat. No. 5,922,849 (1999); Keyes et al., U.S. Pat. No. 6,084,079 (2000); Ashley et al., US 2002/0025936 A1 (2002); Ashley et al., US 2002/0094962 A1 (2002); Carreras et al., US 2002/0192709 A1 (2002); Ito et al., JP 60-218321 (1985) (corresponding Chemical Abstracts abstract no. 104:82047); Santi et al., U.S. patent application Ser. No. 10/648,946, filed Aug. 26, 2003; Carreras et al., US Provisional Patent Application No. 10/920,170, filed Aug. 24, 2004; Omura et al., “Gastrointestinal Motor-Stimulating Activity of Macrolide Antibiotics and the Structure-Activity Relationship,” J. Antibiotics (1985), 38, 1631–2; Faghih et al., “Preparation of 9-Deoxo-4″-deoxy-6,9-epoxyerythromycin Lactams ‘Motilactides’: Potent and Orally Active Prokinetic Agents,” Biorg. & Med. Chem. Lett., 8 (1998), 805–810; Faghih et al., “Synthesis of 9-Deoxo-4″-deoxy-6,9-epoxyerythromycin Derivatives: Novel and Acid-Stable Motilides,” J. Med. Chem., 1998, 41, 3402–3408; Faghih et al., “Entry into Erythromycin Lactams: Synthesis of Erythromycin A Lactam Enol Ether as a Potential Gastrointestinal Prokinetic Agent,” Synlett 751 (July 1998); and Lartey et al., J. Med. Chem., 38, 1793–1798 (1995), “Synthesis of 4″-Deoxy Motilides: Identification of a Potent and Orally Active Prokinetic Drug Candidate”; the disclosures of which are incorporated herein by reference.
A number of parameters are relevant to the development of erythromycin analogs as motilides. Firstly, the evolution of the erythromycin scaffold in the natural producing organisms has been driven by antibacterial efficacy and not by prokinetic efficacy. Therefore, considerable room remains for optimization of the structure-activity relationship for motilin receptor agonist activity. Secondly, it is in fact undesirable for a motilide to possess antibacterial activity. The GI tract is host to a large population of bacteria, whose exposure to a motilide having antibacterial activity may induce the development in them of resistance to erythromycin antibiotics. Thus, a motilide desirably has enhanced prokinetic activity engineered in and antibacterial activity engineered out. Thirdly, a drawback commonly found among motilides evaluated to date is their propensity to desensitize the motilide receptor, meaning that, after the initial dose, subsequent doses of a motilide elicit a weaker or no response (tachyphylaxis). Fourthly, stability and bioavailability are concerns—witness the ready degradation of erythromycin A in the stomach and the lack of activity in its secondary degradation product. Fifthly, some compounds in the erythromycin family have been reported to have undesirable pro-arrhythmic effects, including the prolongation of the QT interval and the induction of ventricular arrhythmias. Limiting these effects to an acceptable level is desirable. Thus, there exists a continuing need to develop new motilides, balancing the various different performance requirements.